The present invention relates generally to integrated circuit (IC) designs, and more particularly to a level shifter that contains single gate oxide metal-oxide-semiconductor (MOS) devices.
As technology advances, the electronic devices tend to be smaller, and their operating voltage tends to be lower. For example, devices made by the 0.18μ processing technology usually operate at 1.8V, and those made by the 0.13μ processing technology often operate 1.3V. These low voltage devices are often built in a circuit system that includes other electronic components operating at a higher voltage level, such as 3.3V. In order for signals to travel between the circuits of various operating voltages, a level shifter is needed to up-shift the signals from a low voltage circuit to a high voltage circuit, or to down-shift the signals from a high voltage circuit to a low voltage circuit.
Conventionally, the level shifter includes both thin gate oxide MOS devices and thick gate oxide MOS devices. The thin gate oxide MOS devices have the same gate oxide thickness as that of the MOS devices in the low voltage circuit. The thick gate oxide MOS devices have the same gate oxide thickness as that of the MOS devices in the high voltage circuit. The thin gate oxide devices interface with the low voltage circuit and outputs signals to control the thick gate oxide MOS devices to generate signals that have the same voltage swing as that for the high voltage circuit. Conventionally, the thick gate oxide MOS devices are necessary to prevent the gate oxide breakdown caused by the high operating voltage.
One drawback of the conventional level shifter is that the switching speed of the thick gate oxide devices is slow, thereby degrading its overall performance. Another drawback of conventional level shifter is that the combination of the thin gate oxide MOS devices and the thick gate oxide MOS devices complicates the manufacturing process, thereby increasing the manufacturing costs.
As such, it is desirable to have a level shifter that contains single gate oxide MOS devices, without using the thick gate oxide devices.